re: Understanding the classical model for linking: You can override an LIB with another LIB, and a LIB with an OBJ, but you can't override an OBJ

Well, in the case of my microcontroller compiler (avrgcc) there is no magic going on, you have to tell the linker explicitly which version you want. The default version doesn't include floating point. If I really want that, I have to include the "printf_flt" library. There's even a third, minimalistic version that supports even less options than the standard one, called printf_min.